1. Field of the Invention
This invention relates in general to the field of adhesive dispensing apparatus which dispenses liquid adhesives and in particular to a filtering arrangement for filtering a liquid adhesive prior to the adhesive entering an adhesive applicator.
2. Description of the Prior Art
Adhesive dispensing apparatus has in the past been used to dispense a liquid adhesive for applying a discrete quantity of the adhesive at predetermined time intervals to such products as paper cartons, baby or adult diapers, rolls of paper towels, rolls of bathroom tissue and other like products. The liquid adhesive is dispensed during the various stages of manufacturing for such purposes as securing the towels or bathroom tissue to the paper rolls, for securing the final wrap of towels or bathroom tissue to the full roll, for fastening together the multiple layers of disposable diapers, etc. Adhesive dispensing apparatus typically includes an adhesive storage or supply tank, one or more adhesive applicator heads, flow lines for connecting the adhesive supply to the adhesive applicator head, a pump for supplying the driving force to cause the flow of the adhesive, and apparatus for controlling the operation of the applicator head to achieve a desired pattern of application of the adhesive.
In the event a hot-melt adhesive is used, the apparatus further includes heating, insulation and additional control means to maintain the adhesive in a liquid state within each of the components comprising the adhesive dispensing apparatus. Hot-melt adhesives generally produce stronger bonds and cure more rapidly than comparable cold adhesives. In commercial production line applications where both high volume and high quality are necessary, hot-melt adhesives are therefore preferred. As previously noted, however, hot-melt adhesives require additional apparatus and controls to assure proper application of the adhesive to a product to achieve the desired result.
In the prior art, it is well known to heat and insulate the supply tank containing the supply of adhesive. It is similarly well known to heat and insulate the flow lines between the supply tank and the applicator head, to heat and insulate the adhesive pumping means and to heat the applicator heads.
One further device within both hot melt and cold adhesive flow systems includes filtering means. Such means serve to filter any debris within the adhesive prior to the adhesive reaching the adhesive dispensing orifice within the applicator head to prevent clogging of the same. Typically, such orifices are of the order of 0.010 inches in diameter and perhaps smaller. It can, therefore, be well appreciated that a dispensing orifice may easily be clogged causing highly undesirable production line shutdowns. Such clogging is thus to be avoided.
The use of filtering means is known in the art of adhesive dispensing systems because such filtering means are very important, if not an absolute necessity, to proper operation of the system. However, in the prior art, the filtering means is generally placed in the system at a location remote from the adhesive dispensing applicator. This is unsatisfactory because debris can be generated within, for example, the flow hose between the filtering means and the adhesive applicator. Thus, regardless of how fine a filter is used, the applicator can still be clogged by the debris generated after the filter and within the system over the considerable distance through which the adhesive must flow prior to reaching the adhesive applicator.
The supply tank typically is a major source of accumulation of particles of debris which in time are forced with the liquid adhesive toward the applicator head. However, in hot-melt systems additional particles can and often are generated by the liquid adhesive within the flow hoses. Such particles are caused by overheating of adhesive which in turn causes it to degrade or char thus developing small solid particles of debris. A filter system immediately downstream of the supply tank and pump would therefore be of no avail to trap and filter the particles which are generated within the flow hoses. A common prior art practice to overcome this problem has been the inclusion of an inline filter between the outlet of the hose and the inlet to the applicator head.
The prior art inline filters have not been completely satisfactory in operation. This unsatisfactory performance is in part caused by the filters not being heated. When an unheated filter is installed between a heated hose and a heated applicator head, a cold spot in an otherwise heated system is created. A cold spot is counter productive to maintaining uniform heating of the hot-melt adhesive. A uniform heat is a very important requirement for satisfactory operation of a hot-melt system. An unheated inline filter will, depending upon the velocity of the adhesive through the filter cool the adhesive below an optimal operating temperature resulting in an increase in viscosity. As the more viscous material continues to flow upstream and through the applicator head, it significantly changes the operating characteristics of the output of the applicator head. This occurs because the size of the flow orifice, the dispensing pattern orifice, the timing sequence and the viscosity of the adhesive all combine to apply a desired size and quantity of a dot of adhesive at a particular location on a product as the product moves past the adhesive applicator head. Consider for example the adverse effect on the manufacture of baby diapers where the change in viscosity would cause an incorrect amount of adhesive to be applied at an incorrect location. Obviously, such a result would be very detrimental. Additionally, the adverse effect of a change in viscosity would be more problematic in slower applications where small amounts of adhesive are dispensed between relatively long time intervals. In these slow applications, the adhesive moves slowly from the supply tank to the applicator head and will remain in the cold area of the inline filter for a relatively long period of time resulting in a significant increase in viscosity of the adhesive.
An ostensible solution to the above problem, that is, providing a heated blanket to an inline filter, is not a satisfactory solution. The inline filter must be removed for servicing from time to time. The advent of a heated blanket would interfere with such servicing. If the blanket were made removable, servicing could be effectuated but not without considerable inconvenience and not without the possible damage to the blanket.
Another prior art solution to the problem of an unheated filter assembly is that disclosed in my copending patent application Ser. No. 06/381,519, filed May 24, 1982 and entitled "Multiple-Outlet Adhesive Applicator Apparatus and Method". In that patent application, a removable filter element is inserted within the heated body of a multiple outlet adhesive applicator head. While such a solution is extremely satisfactory for the type of applicator head described therein, it is not applicable to the majority of single outlet or multiple outlet applicator heads presently in use today.
Accordingly, a primary object of the present invention is to provide a heated filter between the inlet of an adhesive applicator head and the outlet of the flow hose connected thereto.
Another object of the present invention is to provide a heated filter between an adhesive applicator head and the flow hose connected thereto which is integral with the flow hose.
Still another object of the present invention is to provide a heated filter between an adhesive applicator head and the adhesive flow hose connected thereto which is heated by the heating element used to heat the adhesive flow hose.
A further object of the present invention is to provide a heated filter between an adhesive applicator head and the adhesive flow hose connected thereto which is insulated to maintain a constant temperature.
A still further object of the present invention is to provide a heated filter between an adhesive applicator head and the adhesive flow hose connected thereto which is removable without disconnecting the connection between the hose and the applicator head.